432 The Outline of Science 



narrowed down by the elucidation of that special acuity of the 

 senses, or whatever it may be, which underlies the "homing" 

 capacity so well known in birds. Recent experiments by Pro- 

 fessor J. B. Watson and Dr. K. S. Lashley have had as their sub- 

 jects the Noddy and Sooty Terns nesting on the Tortugas Islands 

 in the Gulf of Mexico. Birds taken from their nests and trans- 

 ported by ship in closed cages were shown to be capable of finding 

 their way back from Galveston (to the east) or from Cape 

 Hatteras (to the north), distances of over 850 miles, or from in- 

 termediate points at sea entirely out of sight of landmarks of 

 any kind. In being taken northwards, too, the birds were removed 

 beyond the limits of the species' natural range, and the absence of 

 any previous experience in that direction was all the more certain. 

 At least, therefore, we must concede a very highly developed 

 "sense of direction" or "bump of locality." 



12 

 PLUMAGE, COURTSHIP, AND MATING 



It does not come within the scope of this work to go into the 

 question of the general classification of birds, neither can we con- 

 sider in detail the characters of bird structure or of feathers and 

 plumage. A bibliography is given at the end of this chapter which 

 will be useful for readers who wish to have more information on 

 these interesting subjects. A volume might be written on any 

 one of them. We cannot pass over altogether, however, the nature 

 of feathers and plumage. 



The acquisition of feathers must have been one of the great 

 steps in the progress of birds towards their present position as the 

 supreme flying animals par excellence. It is indeed but to forge 

 another link in that evolutionary history to find that feathers are 

 modified scales and therefore closely akin to the typical covering 

 of reptiles. Let us notice, too, that the unfeathered parts of a 

 bird bear ordinary scales, the one form, as it were, simply replac- 



